


Paper Thin

by snasational



Series: Paper Verse [2]
Category: Undertale (Video Game)
Genre: Alternate Universe - Canon Divergence, Alternate Universe - Crosstale | XTale (Undertale), Cross Sans/Classic Sans, Explicit Sexual Content, Implied/Referenced Self-Harm, M/M, Other Additional Tags to Be Added, Slow Burn, Underverse, Xtale Chara - Freeform, Xtale Sans - Freeform
Language: English
Status: In-Progress
Published: 2020-12-29
Updated: 2021-01-03
Packaged: 2021-03-10 20:14:17
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 7,191
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28403052
Author URL: https://archiveofourown.org/users/snasational/pseuds/snasational
Summary: In an act of kindness, Sans saves Cross from his destroyed universe. He isn't prepared for everything that comes after that.
Relationships: Sans/Sans (Undertale)
Series: Paper Verse [2]
Series URL: https://archiveofourown.org/series/2080206
Comments: 23
Kudos: 127





	1. The Morning After

**Author's Note:**

> HAHAHA i did it!!!!!!! I'd like to thank Ginger and Del for helping me out a bit on this. I'm already having so much fun with this story!! But, fair warning, buckle up! This fic is going to be a long one. I hope to update at least once a week. 
> 
> This fic starts off kind of soft and domestic. But, it's supposed to detail the evolution of Classic and Cross' relationship while also fitting into the events of Underverse. 
> 
> IMPORTANT! You should probably read the oneshot that inspired this whole thing. It's the first thing posted to this series! And hey, while you're there, maybe check out my other oneshots <3 I hope you enjoy! 
> 
> CHAPTER TAGS:
> 
> Vaginal sex, cunnilingus, knotting, implied/referenced self-harm

Sans is normally a late to bed late to rise type of person. He doesn’t like getting up early if he can help it, and he damn sure doesn’t like waking up at any time before ten. But he’s not exactly a light sleeper, either. So when Cross sits up next to him at the ass crack of dawn (theoretically, seeing as Snowdin has no sun) Sans stirs. 

“What the fuck are you doing up so early?” Sans mumbles sleepily, turning his face into the pillow. Usually, he doesn’t curse but in the early mornings the grogginess tends to loosen up his tongue. 

Next to him, Cross snorts. “It’s only four.”

Sans chokes. “Only  _ four?... _ Like, in the  _ morning _ ?” He sits up on his elbows and levels Cross with the nastiest glare he can manage. Although the heat of it is diminished when he catches sight of the other skeleton. Sans is a bit taken back. He had almost forgotten about what happened the night before, but the wounds on Cross’ neck paint a rather graphic picture in his head. 

He cannot believe he actually did that. Sans makes it a point to stay as far away from pointy objects as possible. Hell, after the kid decided to stay with him and Papyrus, he made the decision to get rid of every knife in the household. Not just for the sake of Chara, but for the sake of Frisk as well. 

Sometimes he worries about the kid. 

Cross shrugs. “Yeah? It’s actually kind of late, to be honest.” 

“...”

Cross frowns. “What?”

Sans is too sleepy to deal with this right now. He sighs and grabs his pillow before chucking it at Cross’ head. “Go back to sleep.” It’s not a request but a command. The skeleton then promptly flops back down. 

“But I’m not tired.”

“I don’t care.” 

Cross grumbles, but thankfully lays back down. There’s blissful silence between them. Sans is almost asleep when Cross rolls over right into his personal space. He tenses and cracks an eye open to glare at him once again. Too. Fucking. Early. The guy is grinning at him and Sans doesn’t trust it at all. 

“Cross.” He warns. 

“Last night was great.” Cross murmurs right in his ear-canal. Oh fuck. Is he horny? At four in the fucking morning? They didn’t even pass out until midnight. That’s what, four hours of sleep? Sans is so disorientated. He mentally cannot handle Cross right now. He’s only known the guy for about twelve hours and already he’s overwhelmed. 

For some reason, he doesn’t mind as much as he thought he would. Minus the waking up at four am part. 

“Buddy, I am way too tired to pop a boner right now.” Sans tells him honestly. Cross huffs but snuggles closer into Sans’ side. 

“That’s okay.”

While Sans isn’t horny enough to actually conjure an erection magic begins to settle in his pelvis. Once again, he sighs. Sans doesn’t necassarily have the energy to fuck, but that isn’t to say he can’t  _ be  _ fucked. Jesus, he’s too old to keep up with this kind of stamina. Cross got off literally less than five hours ago, and here he is begging for more. 

“You can top, I guess.”

With the excitement of a child on gyftmas, Cross sits back up and yanks the covers off of Sans. He’s still naked from last night. A faint blue glow fills the room and Cross takes in his unformed magic. 

“It’s so pretty.” He tells him earnestly. Sans squirms under the attention.

“Nothing is even there yet, pal.” 

A finger traces his pubic tubercle. Sans shudders, and slowly a pussy takes shape. He has always loved the feeling of his pelvic bone being touched. No magic, no clothes, just straight contact. It’s a unique sensation, one that he takes great joy in doing to himself late at night. He figures Cross does the same thing, them being the same person and all.

That’s still kind of a weird concept to him. They don’t feel anywhere near the same. He finds relief in this, his sense of individuality still intact. But, on the same coin, he’s confused as to why just so much is different. 

If they’re the same, they should act the same. Right? God, it’s too early to be having an existential crisis. 

A phalange moves to his clit and begins to rub in a torturously slow motion. Sans bites back a whine. Instinctively, he spreads his femurs and allows his magic to form thighs. Cross makes an appreciative noise and maneuvers himself to where he’s in between Sans’ legs. 

“Remember to be quiet.” Sans reminds him, thinking of Frisk and Papyrus. He’s already concerned about the noise from last night. 

“Right, of course, I can do that.” But Cross is grinning mischievously and it does not bode well for Sans. The other leans down and presses their teeth together. That wonderful finger of his moves and grips onto the chub that’s on his hip. “But, can  _ you?”  _

Sans is a very quiet person, thank you very much. He doesn’t dignify Cross with a response and instead turns his head away from the kiss. He’s tired and horny all over again, and this time there’s an extra layer of agitation dictating his mood. If Cross wants to be an ass, he’ll let him but he sure as hell won’t be happy about it. 

Cross pouts. But, not one to be discouraged, he summons his tongue and licks the side of Sans’ cheekbone. The skeleton balks and shoves his hand in Cross’ face. “That is so gross.” He informs him. 

Cross looks like he could care less. He sticks out his tongue again and laps at his fingers. Sans grimaces, but he does drop his hand and allows Cross access to his face again. Oral fixation, his brain supplies while he tries not to cringe at the feeling of slobber on his face. He’s not aroused enough to enjoy that kind of sensation yet. But, after a while Sans relaxes and begins to enjoy the lapping, even if it is kind of weird. Cross moves slowly, down the vertebrae of his neck and across his sternum. Sans closes his eyes and basks in the attention he’s receiving, his earlier sourness being replaced with contentment. 

Before Cross reaches his formed stomach, he pauses. Sans opens an eye and looks downwards at Cross with an annoyed expression. But Cross isn’t looking at him, he’s staring at the chips in his ribcage. There’s something sad in his face and the last thing Sans wants his pity. However, Cross doesn’t comment on them, nor does he touch them. 

That’s right. He understands, doesn’t he? The pain. The embarrassment. Cross gets that side of Sans like no one else ever will. They’re both kind of fucked up, aren’t they? Even if it’s for very different reasons. 

A kiss to his hip has him jerking out of his thoughts. “Cross.” He whispers, the tone begging for him to do something other than lavish him in gentle affection. Too wholesome, Sans is nowhere near ready for that kind of relationship. Especially not with someone he hardly knows. 

He thinks briefly back to that empty field of nothingness. Nobody. No touches. No comfort. He gets it, the guy is probably so affection starved that he falls in love with the first bit of kindness he receives. He can’t really fault Cross for that. And, maybe, if he were in a better headspace, he’d be all for this. 

Sans would just be a burden in the long run. Cross will realize that soon. He’s got goals bigger than life itself while Sans is just a pawn to be used when he needs help. He can’t really offer much more than that. Sans might seem cool and mysterious, an enigma to be picked apart and studied, but the truth is he’s just a guy with too many issues to count. 

Cross doesn’t deserve that. He’s got such a soft soul. Sans doesn’t need to see it to know it. But damn, this guy is determined. He kisses all around the chub of his stomach and strokes his thighs. 

Sans needs to stop this. The first night was fun, but it was just his neglected body telling him to take care of it. This morning is different, there’s really no reason as to why this is happening. He wills himself to open his mouth and put this whole thing to an end. 

“Cross-”

“I know I already said it, but I’m so thankful for you.” Cross says, his mouth still pressed against Sans’ conjured skin. Sans can’t see his face from this position. “You saved me, and now you’re going to help me save  _ them _ . Because of you, I have hope again.”

Oh. What is Sans supposed to say to that? “Glad to hear it.” He utters instead of the entire speech he was planning over why they can’t do this anymore and how he’s happy to remain friends. 

Cross beams at him. He seems to redouble his affectionate skeleton kisses. All the way down his legs to where his magic stops at the kneecaps, all the way back up, and around his groin. Everywhere but the place Sans wants his mouth. Cross is a sucker for foreplay, apparently. But now Sans is soaked with nothing stimulating his aching cunt. 

He’s about to complain but Cross is two steps ahead of him. That hand is back on his cunt again, rubbing his labia in an unhurried manner. The other hand that rests on his thigh pushes at it until Sans’ pussy is spread open. Cross leans back so he can get a good view of what it looks like when he plays with Sans’ slick folds. He watches with fascination, mesmerized by the way the organ reacts to the movements. 

What is Sans, a fucking science project?

“I’ve never fucked anyone before.” Cross suddenly confesses. Sans gawks at him. 

“You really like bottoming that much?” Personally, Sans likes a balance of topping and bottoming. Well, actually, scratch that, usually when he bottoms all he has to do is lay there and take it. But Cross doesn’t seem to be the type to want to be pampered in bed. He’s way too damned confident for that. Sans eyes the cuts in Cross’ neck at the memory from last night. 

“I’ve only ever ‘bottomed’ once.”

Realization hits Sans like a bullet. He stutters, his face flushing blue. “Are you telling me what I think you’re telling me?”

Cross blinks innocently. And then he swipes his thumb across Sans’ clit, which causes the other skeleton to fall back onto the pillows as he tries to suppress a moan. “What? That you took my virginity?” 

There’s no way. Sans slid in way too easily last night. Or maybe Cross was naturally loose? But they shared the same body. Sans remembers his first time being in his college dorm and he actually cried from how much it hurt. Granted, wolf monsters tended to be bigger than normal. Still, Sans isn’t small either. 

“Are you for real right now?”

Cross smiles and nods. “Dude, yeah! It did kind of hurt, to be honest. But training for the Royal Guard built up my pain tolerance.” 

That, and there’s the fact that Cross obviously enjoys a little bit of pain if the knife was anything to go by. “So you’ve never had sex before me?” 

“Nope. Never really wanted to. But i’ve read like, tons of books and stuff on it.”

Books about getting fucked while having a knife shoved against your throat, he assumes. This version of himself has some deeply rooted issues that Sans can’t top. That’s a lie. But still, getting your virginity taken by yourself while being held at knife-point would definitely make a great party story. 

Grillby is going to love this one. 

“But, what-  _ Cross!”  _ He yelps when a tongue replaces Cross’ phalange. 

“Enough talking. There are people still sleeping, remember?” 

Sans whimpers at the experimental lap Cross gives his clit. He does it again, but this time more confident than the last. A few more licks and Sans is already squirming on the bed. Damn, his cunt is overly sensitive after being abandoned for so long. It’s easier to jack off than it is to finger fuck yourself, so Sans never conjured it during masturbation sessions. 

Cross starts to lick at his opening. He slurps at the liquid that seeps out of it and the resulting noise is embarrassingly lewd. Despite being a virgin beforehand, Cross is surprisingly good at eating pussy. Sans supposes that it’s a talent some people are born with. It doesn’t take long for him to get close to the edge under Cross’ eager exploration. 

His hands ball up into the sheets and his breathing is shallow and shaky. But, for the sake of the house, he remains as quiet as he possibly can. 

“Buddy,” He whispers urgently. His pussy clenches around nothing. Sans will have to teach him how to tongue fuck later. “I wanna cum around your cock.” If he cums now, he won’t have any energy to continue and then Cross will be left with blue balls. Or...purple balls? They don’t have the same color of magic. 

Cross reluctantly eases back. A gust of air hits Sans’ pussy and makes him shiver. “Are you ready, then?” 

“I was ready from the get go.” Sans huffs. But he softens at the nervousness emanating from Cross. “Come on buddy.” He soothes, letting go of the sheets to place one of his hands atop of Cross’. “What happened to earlier? You were so eager to jump my bones.”

“I still want to!” Cross quickly assures.

“Well?” Sans raises a brow bone. “Get on with it then.” 

Cross nods, although the tension seems to have left his form. He shuffles forward again and Sans gets a good view of Cross’ conjured body and admires it. He’s not chubby like Sans is, the muscles of his ecto well defined. But, their cocks are more or less the exact same. Weird. At the end of Cross’ penis sets a swell of magic.

Is that...a knot?

Sans blinks. Hm. Yeah, that’s even weirder. But, he knows from experience how great being knotted can feel. When he first moved to Snowdin, he and Doggo had more than a few drunken nights together. And then there was that time Dogamy and Dogaressa. Good memories, but after he was done fucking around Sans never gave the knots a second thought.

Until now, of course. Sans can feel wet magic building up in his mouth. Cross guides himself to Sans’ dripping entrance and sinks in with no resistance. They both groan, and Cross trembles slightly. The grip on his hips start to sting, phalanges digging in with abnormal strength. As opposed to being turned off by the pain, Sans is only more aroused. His own hands circle tightly around Cross’ wrist bones, holding on. 

“Dude.” Cross whimpers. “This feels awesome.” 

Sans hums in agreement. He gives his hips a little roll to encourage Cross to start moving. And he does, slowly building up a steady rhythm. Sans hooks his legs over his waist and pulls him even deeper inside his depths, which in turn elicits a mewl from Cross. His dick twitches violently. 

“You’re so tight.” He says through grit teeth. 

Yeah, being celibate for over a year does that to a person. Sans doesn’t tell him this and instead clamps down even tighter around Cross. Cross hisses, but it only serves to make him drill into Sans harder. The slowness from earlier is gone, the gentle rocking of his hips replaced by shallow thrusts that hit directly against Sans’ spot. 

Cross must realize his angle is perfect from the way Sans begins to cry out. He picks up the pace, angling his hips to jab that wonderful area over and over again. Magic builds inside before releasing violently. Sans’ eyelights fizzle out from the force of it and he has to bite down on his tongue to prevent him from screaming the whole house down. 

“Ngh, holy fuck. Cross, you have to- shit! Cross, I can’t! Too much, too much!” Sans claws at hands that are still gripped onto his hips. Too many sensations are going through him right now, the pleasure quickly becoming raw and unbearable.

But Cross doesn’t stop. His expression is blissful, those beautiful eyelights hazed and his jaw dropped open. Purple drool falls down the corners of his teeth, and he’s so flushed that even the magic fusing his joints together begins to glow brightly. He looks like an addict getting his fix. This isn’t healthy, Cross might become obsessed with this if Sans isn’t careful. Using sex as a coping mechanism isn’t a good idea.

But, hell. He couldn’t even prevent Cross from having sex with him in the first place. What makes Sans think he can do it after they’ve both had another taste at it? Last night was different, it didn’t have this electric vibe that fizzles between them. 

This is too much. Sans closes his eyes and he goes limp on the mattress. He lets Cross have his way with him, too tired and overstimulated to do anything else. After a few more strokes, the knot begins to catch on the rim of his pussy. Another stroke, and it’s popped inside of him. Cross groans glutteraly, his breath hitching in the middle when it swells and fills Sans up to an unbearable amount. 

The amount of cum pumped inside of Sans is near unbearable. He feels so full right now, his entire body tingling and his stomach heavy with the weight of Cross’ jizz. 

“Dude.” Cross practically sobs. Sans mutters gibberish in response, way too fucked out to say anything intelligent or witty.

That iron grip lets go of his hips and Cross falls on top of Sans. He twitches and shudders every few seconds. Sans doesn’t even have the energy to hold him back. Inside, that dick still pulses weakly and the knot stays firmly in place. With the dogs, it took about fifteen minutes for the knot to reduce enough for them to comfortably remove their dicks. Sans wonders how long it’s going to take for Cross’ dick to give him mercy. 

Finally, he musters up the will to say a few things. “Will you go back to sleep now? If  _ knot  _ I think I'll die.”

Cross mumbles something sleepily. Sans takes that as a good sign. He looks at the clock that sets on his dresser, which reads 5:25am. Still way too fucking early. He doesn’t ever want to leave his bed again.

*

Cross wakes him up again at seven. Sans curses his very existence. Of course he gets saddled with a crazy version of himself who insists on waking up at ungodly hours. Didn’t he say something about the Royal Guard? It makes sense, the lot of them are crazy. Aside from Papyrus, of course. 

“Why do you keep waking me up?” Sans whines like he’s eight and not thirty three. He pushes his head back into the pillows and wills Cross’ entire existence away. 

“You can’t sleep in any later.” Cross reprimands. “Wasn’t it you that said we had a busy day today?”

“I did.” Sans’ voice is muffled by his pillow. “But I never wake up until at least ten.” 

Cross makes an offended noise. “That’s so lazy! Come on, we need to take a shower and make ourselves presentable.” 

“I wasn’t the one who wanted to fuck at four in the fucking morning.” Sans reminds him. He makes no move to get up. Cross is quiet for a moment and he considers that a win. 

“Where’s the bathroom?”

“Very end of the hall to the right.” 

The mattress squeaks as Cross gets up. There’s the sound of clothes being picked up, and then footsteps leaving the room. He opens the door as quietly as he can and Sans sighs happily. Great, he can go back to sleep now that Cross isn’t here to nag him awake. His bones still ache, and his pelvic area feels like it’s on fire. 

Sans is never leaving this bed ever again. 

But not even five minutes later Cross is back in the room. Sans bemoans the shortcut that led him to meeting this horrible monster. Truly, this man has to be the cruelest person he’s ever met before in his life. But, Cross says nothing. He just pads back over to Sans and pulls the covers off of him. 

Sans reaches for them, radiating displeasure. Sadly, Cross has thrown the covers to the other side of the room. The mattress dips. Sans glares nastily in his direction. “Buddy, if you don’t leave me alone I swear you’ll- Hey!” 

Cross picks him up. Like, he  _ actually  _ picks him up like he’s a sack of potatoes. He hooks his arms under Sans’ patellas and lifts him into his arms. Sans has murder on his mind as he scrambles to balance himself on Cross’ shoulders. 

“Sorry.” He doesn’t sound very sorry at all. “But I’m not going to meet this world looking like this and neither are you.”

Sans doesn’t respond because he knows he’s right. It doesn’t mean he has to be happy about it, though. How would he explain the mess to Papyrus? To  _ Frisk?  _ That is one awkward conversation he’s not ready for. Having to explain their new housemate is already going to be one hell of an experience, he can’t imagine having to confess to fucking a cartoonish clone of himself. 

They walk through the hallway undetected. Papyrus’ door is shut, which is a miracle. It means he’s either still asleep or not in the house. When Cross carries him into the bathroom, a bath is drawn. Sans thanks the stars that they remodeled the bathroom to be spacious enough for Papyrus last year. 

Maybe he can get away with a nap in the bath. 

Cross sets him down in the water gently before stepping into the bath himself. He sighs blissfully at the warm water against his bones, his eye sockets closed. Sans is still kind of pissed off at his second rude awakening so he just sits there with his arms crossed. Admittedly, the water does feel nice. He normally just showers and calls it a day. 

“...Hey.” Sans says after a few minutes of them simply soaking. “You said you were training for the Royal Guard?” 

Cross’ whole body tenses. “Did I?”

Sans tilts his head at the odd behaviour. “...Nevermind.” It’s obviously something he wishes to leave in the past. Sans can respect that. The skeletons in his closet are numerous, they could form their own nation by this point. 

“You’re too nice to me, dude.” Cross whispers. He pulls his knees to his chest like he did yesterday when they first met. 

“Nah. Everyone deserves a bit of kindness.” 

This doesn’t seem to comfort Cross at all. “If you knew what I did you’d be saying something different.” 

Theoretically, Sans could poke and prod until he got all the answers he wants. But Sans is not Gaster, he knows how to be sympathetic. Cross is a living being, not a specimen that needs to be figured out. It’s clear as day that he’s not ready to talk about what happened in that void of nothingness and Sans isn’t going to push it. 

“I mean, it’s not really my business so…” He waves his hand in the air. It causes water to splash a bit. “Anyways, you’re totally going to love my bro. He’s the coolest. And you’ll probably like Frisk, too. They're a little weird to be honest but I still love them all the same.” 

“...I see.” Sans can’t put a name to it, but he swears he saw pain written all over Cross. Fuck. Sans is really good at saying all the wrong things. But Cross smiles at him, another emotion Sans can’t quite name softening the edges of it. “I can’t wait to meet them.” 


	2. Imperfection

**Summary for the Chapter:**

> “...You know. I hated you.” Cross speaks up suddenly. He’s doing that thing where he’s looking nowhere again.

**Notes for the Chapter:**

> this was a stress relief chapter 
> 
> Not Proofread or Beta'd!
> 
> Chapter Tags:
> 
> Oral Sex

Both Cross and Sans are already seated at the table when Papyrus comes down stairs at eight. Cross has ditched his overly complicated jacket upstairs, and without it he looks less like one of Alphys’ drawings and more like...well, a normal person. The way the black undershirt hugs his ribcage makes Sans feel a bit perverted for looking. It’s not like Cross has anything that he hasn’t seen before, but to openly gaze feels wrong. 

Cross doesn’t look affected by any staring, though. He sips quietly on a mug of hot chocolate, the skeleton’s gaze a million miles away. He pays no attention to the way Sans’ eyelights trail over his scarred face. Sans wonders what he’s thinking about. His world, possibly? Sans hopes he isn’t regretting anything that they’ve done together. He’d feel like the world’s biggest jackass for the hundredth time in the past twenty four hours. 

But Cross seemed fine when they were getting dressed? And, the more he studies him, the more Sans realizes he looks less anguished and more nervous. The hand holding the mug trembles slightly.

(A trembling hand grips a coffee cup.  _ World’s Awesomest Brother  _ is written in sharpie, the sloppy lettering a trademark to a child still learning how to write. 

“You’re wrong.” Sans tells him firmly, but the shake in his voice gives him away entirely. “Professor, there’s no possible way.”

The man hums and stares at a chalkboard, analyzing various equations. Sans’ eyelights are glued to the board as well, and his soul sinks the more he reads. “And what will you do if I’m right, Sans?”

Coffee spills from the sides of his mug.)

“You doing good, buddy?” Sans asks casually. He props his elbow up on the table and rests his cheekbone in the palm of his hands, feigning nonchalance. 

Cross breaks his staring contest with the wall to glance at Sans. “Yeah, I’m good.” 

Sans is not an idiot. But also Sans doesn’t really like pushing subjects, his lapse of judgement in that empty space aside. “Okay.”

A few minutes pass by. Sans can hear Papyrus rummaging around upstairs. It’s weird that he still hasn’t come out, actually. It might have been one of those nights where his brother actually slept good. Those are rare. No amount of sleep medicine or natural remedies have ever worked on him, either. 

He remembers last night and this morning and has to fight down a flush. Stars, he prays that Papyrus was in deep sleep for all of those times. 

Cross’ shaking intensifies and Sans realizes that yeah, maybe he is an idiot. Cross is nervous about meeting Papyrus! He can’t imagine why. Was Cross and his brother not on good terms before the destruction of their home? Maybe, as awful as it sounds, Cross is an only child? Sans assumes Papyrus is great in every universe, there’s no reason for him to be so spooked about the prospect of meeting him. 

“It’s going to be okay.” Sans tells Cross before footsteps begin to stomp downstairs, because he can’t just not say anything. Cross flinches at the noise. 

Soon, Papyrus strolls through their living room. He doesn’t notice the two skeletons at first, too focused on his goal of making breakfast. He walks right into the kitchen and then has to do a double take. 

“Sans?” He asks in disbelief. It’s like he doesn’t even see Cross. Which actually works out great because Cross freezes at the sight of Papyrus, his mouth twisted into an upset frown. 

“Uh, yeah bro?” 

“What are you doing up so early?” 

Sans makes it a point to not look at Cross. He doesn’t think his brother would talk kindly to  _ ‘oh, well, this guy got horny and decided to take it out on me at four am.’ _

“Um. Well, we have company so…” He trails off, hoping his brother will fill in the gaps. Thankfully, Papyrus takes to the bait. 

“Oh!” His attention is on Cross now, who shrinks back a bit at having Papyrus notice him. “My goodness, how rude of me! I didn’t even notice you were there! I am the Great Papyrus! And you are?” 

Cross toys with the edge of his sleeves and looks at anywhere but Papyrus. “...Cross.” He mumbles. He hides his face in his turtleneck. 

_ Cute,  _ Sans’ head tells him before he can stop the thought. 

“Cross? What an exceptionally cool name! It is almost as cool as the Great Papyrus’ name!” 

“Nothing can beat that, bro.” Sans pitches in.

Papyrus preens under his brother’s praise. “Yes, I am quite aware. Anywho, you are a skeleton, correct? I didn’t know there were any of us left! Where did you come from, Cross?” 

Shit. Sans totally forgot to come up with an explanation for that. Papyrus is right, there’s no other skeleton left in the underground except for the two of them. Cross looks desperately to Sans, and in response he blurts out the first thing that comes to mind. 

“The ruins.”

Both Cross and Papyrus wear a puzzled expression. 

“The ruins? But nobody except for humans ever comes from the ruins, Sans.” 

“Cross here has lived there his whole life. Plenty monsters still live there, Paps.”

“...Yeah.” Cross agrees. “I...Um, I wanted a change in scenery so I came to Snowdin.”

Sans is immensely relieved when Cross goes along with his lie. Papyrus brightens. 

“Wowie! That’s so cool! I didn’t know monsters still lived in the ruins like that. Welcome to Snowdin, Cross! My brother and I would be more than happy to host you while you adjust to life outside the ruins. We-“ Papyrus pauses. “Well, we  _ had _ a spare bedroom. Sans, where is Cross going to sleep?” 

“It’s cool bro, Cross can sleep in my bedroom.” 

If Papyrus had a nose it would be scrunched up. “But your room is disgusting, Sans!” 

Cross snorts. 

Hey, don’t blame Sans for the fact that trash doesn’t pick itself up. Used to the criticism, he shrugs and changes the subject. Sans is aware that his room is gross, but to be honest he doesn’t really care enough to have it be the center of attention. “What’s for breakfast, bro? Wait, lemme guess...leftovers?” 

“Oh! I had almost forgotten about breakfast! No, I am afraid we will not be having my spaghetti. Regrettable, I know. But It’s a surprise, since our new friend and our other new friend will be staying with us!” Papyrus hurries into the kitchen and the sound of pots and pans clinging together can be heard.

Cross stares after him, his expression morose. Sans can’t stand that look on his face, because he’d personally never have the audacity to look that sad. “Come on, I wanna show you something.” 

Cross blinks out of whatever weird trance he’s in. He doesn’t have time to react when Sans grabs his hand and promptly teleports them into his workshop. Cross stumbles when Sans lets go, disorientated from the sudden shortcut. Sans should’ve warned him beforehand, and now he feels guilty  _ again.  _

“Sorry.”

Cross recovers from his dizzy spell quickly. “No, dude, you’re fine. I just wasn’t prepared for...uh, whatever that was. You did it last night too. What is that?”

The manipulation of atoms. If you split them at just the right amount, you can step through the void and go wherever you wish. Sans is the only one to ever accomplish this, and he doubts someone who doesn’t understand a damned thing about quantum physics would be able to do the same thing. So, Sans shrugs. 

“Magic.” He says, even if it’s less magic and more science. “This is my workshop.” Well, what remains of it at least.

Sans had crammed all of his projects in the drawers and sold all of the furniture that used to decorate his work space. Cross looks around curiously. Predictably, his eyes catch on the draped machine.

Sans closes his eyes and fights against a wave of negative emotions. 

(“Isn’t it beautiful?”

Sans rolls his eyes. “It’s a box made of scrap metal.” 

That smile makes Sans shiver.)

“What is that?” Cross inquires as he steps deeper into the desolate room. He takes in every little detail attentively. Cross would’ve made a good scientist. He’s lucky that he’s not, though.

Sans stuffs his hands in his pocket. “Broken. Don’t mind that, it wouldn’t help us anyways.” That’s possibly a lie. Truth be told, Sans doesn’t actually know what the damned thing is capable of at all and he has no desire to find out either. 

“Oh.”

“Mhm.”

“...” Cross sighs and leans against the workbench. “Aren’t scientists supposed to have lots of stuff in their labs?”

“Yeah, if this was a lab. It’s a workshop, I need to unpack it and organize everything before we can actually use it.” Sans would rather bite off his own leg than go through all of the books and files crammed into those drawers. Don’t even get him started on the blueprints he’ll have to sort. This is such a pain. 

“...You know. I hated you.” Cross speaks up suddenly. He’s doing that thing where he’s looking nowhere again. Sans blinks. Ouch. They’ve only known each other for like, what? Under a full day? 

“Or, well. I thought I did. I’m supposed to be a perfect version of you. But...but for some reason, your world is so much better than mine.” Oh. So Cross definitely knows way more than he’s been letting on. Sans isn’t at all surprised by this. He lets Cross continue speaking.

“I saw you once. On the surface. Your world...it’s called the Main Universe. You all looked so...happy. So perfect. And I hated you so much for it.”

Sans will be honest. He has no idea what Cross is talking about in terms of universes. He’s got a vague feeling that he’s not supposed to know, either. But, hey, cool to know that Alphys’ nerdy ramblings about ‘Alternative Universes’ are real. Although, less coffee-shop orientated and more tragedy leaning. 

He disagrees with Cross on the perfect part. “But how can I hate you now, knowing what you’re really like? I’m a product of failure and you...you’re the real deal. I should hate you. Why can’t I hate you?” The last bit is whispered harshly as he stares down at his hands. 

When he doesn’t say anything else, Sans figures it’s his turn to speak. “There is no such thing as a perfect world.” Cross’ eyes snap up to look at Sans, but the skeleton is studying the tarp that covers his greatest fear. “To try and achieve perfection is...dumb. Totally pointless.”

“Besides, as you can tell, we’re not on the surface. Are resets not a thing for you?”

Cross frowns and tilts his head. How lucky. 

“Topic for another time. Anyways, glad you don’t hate me anymore.” He focuses his attention back on Cross and winks out of habit. Cross’ face turns purple at record speeds. 

“I...don’t push your luck.” He crosses his arms and huffs. There’s no heat behind it. Playfully, Sans creeps towards him. 

“Aw. Don’t be like that.” Sans stops once he’s standing in front of him. “I’m  _ sans _ ational. What isn’t there to love about me?”

This pulls a small laugh from Cross. “Laziness. Messy room. Sleeping in late. You snore-”

“Hey, hey, woah. I most certainly do not snore.” Right? Sans inwardly frowns. Well, fuck. He owes an apology to every single one of his one night stands. 

“Sure.” Cross agrees unconvincingly. “You totally do not.” 

“Hm. That’s sarcasm I hear.”

He smiles innocently. “Me? Never.”

Silence lapses between them as they make eye contact. Something warm floods through Sans, a feeling he hasn’t felt in years. There’s an irresistible pull and he finds himself leaning forward to lightly peck Cross on the teeth.

That’s okay, isn’t it? Whatever he and Cross has going on, it far exceeds platonic affection. Less than a day, he reminds himself. Cross doesn’t know him and he doesn’t know Cross. Except maybe Cross has known him for longer than Sans knew about previously. Still. 

Cross presses back gently. All logic leaves Sans. He must be cursed or something. Definitely the doing of Cross’ dick. 

Sans gasps when arms wrap around him to pull him close. The movement isn’t sexual in nature, but there’s a desperate clinginess that makes him feel hot and heavy. No way can Sans go another round, he’s too old for his magic to react on command like that. However, he can probably get Cross off.

He breaks off this soft kiss. “Yeah, my body isn’t ready for another round but I can um. Suck your dick, I guess.” Fuck, that sounded so much more confident in his head. 

“Dude, you don’t have to if you don’t want to.” 

Sans waves him off. “Nah, I want to. Sit up on the counter, I won’t take long.” He’s got the best mouth in Snowdin. Almost all of the sentries would agree with that sentiment. 

Cross doesn’t say a word as he jumps backwards onto the workspace. Sans grins and pecks his teeth again before undoing Cross’ belt with skillful hands. It comes free quickly, and so does Cross’ cock. Sans gives it a few strokes and relishes in the way the skeleton shivers underneath his touch. 

“Ever been sucked off before?”   
  


Cross blushes and shakes his head. Oh yeah, he’s not lasting any longer than five minutes. Sans drops to his knees and wastes no time in conjuring up a tongue. He goes in strong, licking at the base where his knot sits. Cross jerks violently at the motion. His cock gives a twitch, beads of precum spilling over. 

Fuck, he’s reactive. 

Sans laps his way up his cock with lazy kitten licks, pausing briefly to tongue veins and spots that he knows are sensitive. It might be a little mean to tease like this, but really it’s Cross’ fault for reacting the way he does. Every hitched breath and soft moan only fuels Sans’ desire to bully him a little bit. 

Finally, he reaches the tip. Aiming for unpredictability, he swallows it down. All the way to that swelled base. He places his thumb in the crease of the knot, kneading softly as he sucks hard. 

“Fuck!” Cross hisses. His hips twitch but he shows surprising self restraint. For someone who was a virgin until recently, at least. “Sans, please, I’m not going to last long.”

Good. He bobs his head between Cross legs and rubs even more. He can taste the precum flowing in his mouth like a river. It’s taste is unique, earthy and almost sweet. Way better than the average joe’s bitter spunk if you asked Sans. Boldly, he swallows around the head of Cross’ dick.

The moan he releases his simply divine. He tenses and jerks a bit before releasing a healthy mouthful into Sans’ waiting throat. Sans happily swallows all of his jizz. When he pulls off the cock with a wet pop, he gives Cross a smirk. “Consider that payback for jumping my bones  _ twice.”  _ __  
  


Cross buries his hands in his face. “Holy fuck dude.” 

Sans barks out a genuine laugh, surprising even himself.

*

“Where did you two go?” Papyrus asks disapprovingly once they walk back into the kitchen. There are four plates set at the table, and on those plates is...eggs? Papyrus has never made an actual breakfast food for breakfast. And on top of that, they look good. 

Sans ushers Cross into sitting down before taking a seat next to him. “Yeah, uh, sorry about that.”

Cross nods. “Yeah. Sorry, dude.” 

Papyrus softens his stance. “Well, I suppose I can forgive the disappearance just this once! I shall go wake the human up. Please, dig in!” 

He then promptly stomps up the stairs, his scarf somehow flowing dramatically behind him as he does. Man, Papyrus really is the coolest person ever. Cross is smiling, but it seems kind of fake. Sans is the king of fake smiles, he can sniff out a fake smile better than anyone on this earth.

“Frisk isn’t bad.” 

Cross flinches. Sweat is beading on his skull. The red eyelight spazzes for a moment. Sans doesn’t know what to make of that. “I never said he was.”

“They.” Sans corrects instinctively. His Frisk must be a male? What an odd difference to have. “Frisk is a good kid. You don’t have to be worried about them snapping on you.” That’s mostly true. Cross doesn’t have to know that.

Cross pokes at the eggs for a moment. “I’m sure Frisk is great.” Again with that miserable tone. Jesus. Cross is determined to make a saint out of Sans. 

“Yeah. They are.” 

Papyrus comes back down, the child cocooned in blankets and cradled in his arms. Their hair is an absolute mess. Sans is going to have to find his comb for them. “Sans! We are going to have to buy the human warmer clothes!”

“Okay.” He’ll take them to the shopkeeper later. Assuming Frisk decides to stick around for a little while. Sometimes, when their control over Chara is stronger than normal, they like to stay in either the ruins or Snowdin for extended periods of time. A little break, they call it. 

Frisk mumbles something sleepily. Sans relates on a spiritual level. 

Cross says nothing. The little nagging fear of his kid being attacked is eased, if just a little bit. He has no idea how Cross feels about his Frisk but it can’t be anything good. Thankfully, Cross’ eyes remain glued to his plate as Papyrus plops Frisk down into a chair. They blink blearily. 

“Morning Sans.” They greet through a yawn. 

“Mornin’, Sunshine. You look awfully refreshed.”

“Sans! Do not tease the human!” 

Sans chuckles. “I’m not, I swear.”

His mood drops a bit when he sees the way Cross is staring at Frisk. Anger, hatred, sadness. Too many negative emotions. Paternal defensiveness swells in Sans before he can stop it, and he lightly kicks his fibula. Cross shakes out of whatever stupor he’s put himself in and glares at Sans.

Sans does not feel bad for him. 

“Who are you?” Frisk asks, wide eyes full of curiosity. Good, they didn’t read the room. For once he is beyond thankful for that. 

“That is ‘Cross’, human! Doesn’t he have just the neatest name?” Papyrus answers, always eager to jump into conversation. 

They nod excitedly. Sans figures it’s because after a dozen resets, something new has finally happened. “I like that name, Cross.” They tell him politely. “I’m Frisk.”

Cross stares. He’s trembling. Already, magic thrums at Sans’ fingertips, ready to freeze Cross’ soul if he has to. But it doesn’t come to that. Cross closes his eyes, exhales, and opens them again with a smile.

“Hi, Frisk. I like that name too.” 

They beam at him. Sans is immensely pleased with Cross. 

**Notes for the Chapter:**

> We'll get to plot. Eventually.
> 
> ALSO mama bear sans!!!! my favorite kind of sans

**Author's Note:**

> I have so, so, so many plans for this fic. You have no idea. I'm so excited to be writing it. 
> 
> Follow me on twitter @ snasational 
> 
> Comments and kudos are always appreciated


End file.
